The present invention relates to a system for controlling the fuel injection in an automotive engine in accordance with engine operating conditions.
In a known fuel injection system, basic fuel injection quantity Tp is calculated in dependency on absolute pressure in an intake passage of the engine and engine speed. A pressure sensor is provided downstream of a throttle valve in the engine for detecting the absolute pressure in the intake passage. The engine speed is detected by a crank angle sensor. In accordance with output signals from these sensors, the basic fuel injection quantity Tp is determined. Actual fuel injection quantity Ti is obtained by correcting the basic fuel injection quantity Tp in accordance with engine operating conditions such as coolant temperature and throttle opening degree.
However, the absolute pressure in the intake passage oscillates because of the pulsation of intake air. Consequently, the basic fuel injection quantity Tp varies in accordance with the pulsation. Thus, the operation of the engine becomes unstable, particularly at low engine speed.
Japanese Patent Application Laid-Open 60-3448 discloses a fuel injection control system. In the system, pressure in the intake passage is sampled at a first timing synchronizing with rotation of a crankshaft of an engine, and further sampled at a second timing having a shorter period than the first timing. The sampled pressures are averaged to obtain a first average pressure and a second average pressure. The first and second mean pressures are selected in accordance with engine operating conditions. In dependency on the engine speed and the selected pressure value, the basic fuel injection quantity Tp is calculated.
However, at a transient state of the operation of the engine, the average pressure PM.sub.AVE based on the pressure PM is produced with a delay with respect to the requirement of the engine operation, as shown in FIG. 7. As a result, the fuel injection quantity differs from the necessary quantity.